There are stories like this one speaking with outrage over investigators not processing "rape kits" containing evidence from sexual assault cases. My question: is the evidence processing backlog specific to rape cases or does it apply across all types of crimes? Here's what I found from the National Association of Attorneys General:

... forensic evidence was collected in 88 percent of homicides, 73 percent of rapes, and 29 percent of property crimes. A considerable number of unsolved cases also contained forensic evidence that was never submitted to a crime laboratory for analysis: 14 percent of open, unsolved homicides, 18 percent of open, unsolved rapes, and 23 percent of open, unsolved property crimes.

Initial impressions of this would seem to indicate police prioritizing resources roughly the same way as a typical person would: - highest priority to murder cases, - somewhat lower priority to various types of assault and battery cases, and then - lowest priority to other crimes.

But wait! There was more:

There are reasons why a law enforcement agency may not submit forensic evidence to a lab. The evidence may be considered not probative, charges may have been dropped or a guilty plea entered.

If I understand the definition of probative it's basically something that serves as proof of a point in question. Of the three categories of crime for which statistics were available: murder, rape, and property crime, rape is the only one guaranteeing that a live victim was present when it happened. In other words, it seems far more likely that the victim could identify the perpetrator with this type of crime than the others, making DNA testing only relevant if a denial ensues when dealing with cases in which the victim is able to identify the one who assaulted her/him.

In other words - surprise! - the "rape kit processing backlog" seems only a particular instance of the more general evidence processing backlog. Priority in evidence processing seems to be about how a typical person would assign it and, of the types of cases for which evidence is available, it seems that forensic evidence would be least helpful in identifying a perpetrator due to the presence of a witness (the victim) who may be able to identify the perpetrator without the cost of DNA processing.

(Note: I'm assuming "unsolved" here means that either a perpetrator has not been identified or that the guilt of the identified perpetrator has not yet been legally established one way or the other.)